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At its peak on September 11, 2017, the ozone hole extended across an area nearly two and a half times the size of the continental United States. The purple and blue colors are areas with the least ozone - Photo: Katy Mersmann/NASA and NASA Ozone Watch

This year, satellite measurements revealed that the giant hole over the Antarctic in the Earth's protective ozone layer shrunk to its smallest maximum-extent since 1988, according to the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA).

NASA announced that the ozone hole shriveled to its smallest peak, about 2.5 times the size of the United States, on September 11.

Paul Newman, Chief Scientist for Earth Sciences at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement: "The Antarctic ozone hole was exceptionally weak this year. This is what we would expect to see given the weather conditions in the Antarctic stratosphere.”

According to NASA, the shrinking was a side effect of the Antarctic vortex, a low-pressure system that rotates clockwise above the southernmost continent, which prevented the proliferation of polar stratospheric clouds in the lower stratosphere.

Precisely, those polar stratospheric clouds lead to reactions catalyzed by chlorine and bromine that destroy ozone.

However, scientists explained that two years of lower-than-usual ozone hole extent is mere natural variability, rather than a sign of faster healing.

The hole in the ozone layer in the southern hemisphere was first detected in the winter of 1985, as the returning sun’s rays catalyze reactions involving man-made, chemically active forms of Chlorine and Bromine, a series of chemical reactions that destroy ozone molecules.

Scientists expect the ozone layer to return to its 1980s size around 2070.